Snap-acting pressure switch



T. A. ANDREW ETAL 3,330,925

SNAP-ACTING PRESSURE SWITCH Filed Aug. 4, 1965 5 Sheets-Sheet l julyl1', W67 T. A. ANDREW ETAL 3,330,925

SNAP-ACTING PRESSURE SWITCH Filed Aug. 4, 1965 5 Sheets-Sheet E' w di NZ a a )Tempera/gra July N, i967 T. A. ANDREW ETAL SNAP-ACTING PRESSURESWITCH Filed Aug. 4, i965 3 Sheets-Sheet 5 United States Patent O FiledAug. 4, 1965, Ser. No. 477,206 6 Claims. (Cl. 200-83) The presentinvention relates generally to electric switches, and it relates moreparticularly to snap-action electric switches which respond to changesin liuid pressure to be actuated from one operating condition toanother.

The improved pressure-responsive switch of the present invention, asindicated above, is of the snap-action type. The switch is constructedso that only when the uid pressure introduced to the switch exceeds aparticular threshold, will the switch snap from a first electricalcondition to a second electrical condition. Conversely, only when thefluid pressure drops below a particular threshold will the switch snapback to its first electrical condition.

The improved snap-action pressure-responsive switch of the presentinvention includes a sealed double-diaphram aneroid snap capsule elementas the actuating component of the assembly. The snap capsule is soconstructed that it utilizes the snap (or over-center) action of one ofthe two diaphragms forming the unit. This snap acting diaphragm operatesin principle similar to that of a Belleville washer, while the otherdiaphragm acts as a yieldable support, the two forming a sealed chamberand both providing motion that results in a maximum overcenterdisplacement. This combination of yieldable supporting diaphragm and aBelleville disk to form an aneroid capsule givesrmuch greaterover-center travel than could be obtained with a single Belleville disk.Basically, this enables larger contact gap in the final pressure switch,giving it the capacity to switch higher currents in circuits having highinductance.

An important object of the present invention is to provide an improvedpressure-responsive snap-acting electric switch of the type mentionedabove, and which is rugged and durable, and yet relatively inexpensive.

Another object of the invention is to provide such an improvedpressure-responsive snap-acting switch which can be accurately andprecisely set to respond to predetermined maximum and minimum pressuresso as to be actuated from one electrical condition to the other.

Yet another object of the invention is to provide such an improvedpressure-responsive electric switch which is not subject to mechanicalor electrical failures, and which is capable of performing efficientlythroughout a long and trouble-free operational life.

A feature of the improved snap-acting pressure-responsive electricswitch of the present invention is the provision therein of a sealeddouble-diaphragm snap-acting capsule as the actuating element, asmentioned above.

The provision of such a snap-acting capsule permits the switch of theinvention to incorporate the desired snapacting diaphragm action withoutthe concomitant production of excessively high stresses at the outerperiphery of the diaphragm. Such high stresses are encountered, forexample, in prior art switches using a single snap-acting diaphragm.

The high stresses, so encountered in the prior art switches, have atendency to produce permanent deformation in the metal at the rim of thediaphragm, with resulting loss in reliability and change of performancecharacteristics in the prior art switches.

When a single Belleville disk is used in the prior art units, thesealing effectiveness is compromised in that a ICC certain amount of thethickness of the disk must be used for the sealing diaphragm. To obtainaccurate performance in such prior art units, the thickness of thesealing diaphragm must be held at a minimum, which creates a tendencyfor leakage due to material porosity and corrosion during theoperational life of the unit.

In the improved unit of the invention, a single sheet of material isused to obtain the over-center or snap action, so that thickness may bemaximized to provide enhanced sealing effectiveness and corrosionresistance.

Another feature of the improved pressure-responsive switch of thepresent invention is the adjustability of the assembly, wherebyoperating thresholds, dead bands, and other switch characteristics, canbe precisely preset to any desired values.

Other objects, features and advantages of the invention will becomeapparent from a consideration of the following description, when thedescription is taken in conjunction with the accompanying drawings, inwhich:

FIGURE l is a side sectional view of a pressureresponsive electricswitch constructed in accordance with one embodiment of the invention;

FIGURE 2 is a side sectional view of a modified construction o-f theassembly of FIGURE l;

FIGURE 3 is a side sectional view of a second modification; and

FIGURES 4, 5 and 6 are curves which are useful in explaining theoperation and characteristics of switches constructed to incorporate theconcepts of the invention.

The pressure-responsive snap-acting switch of the present invention may,for example, have a generally cylindrical configuration and the switchmay be enclosed by a switch housing lti.

The switch housing 1t) has a first end casing 12 welded,v

or otherwise attached to its right hand end, by means, for example, of aweld 14. The casing 12 supports, for exam-- ple, the electric terminalassembly of the switch.

The housing 10 also has a second casing 16 welded, or otherwise attachedto its right hand end in FIGURE l by means, for example, of a weld 18.The casing 16 constitutes, for example, a fitting for the switch, theiluid pressure being introduced through the right hand end of the tting.

A sealed double-diaphragm snap-acting cartridge 20 ismounted on theinner face of the casing 16 by means, for example, of a weld 22. Thesnap-acting cartridge 20 includes a first diaphragm 2a and a seconddiaphragm 26, the two diaphragms being sealed to one another, forexample, by means of 'a peripheral weld 28.

A plunger assembly 30 is slidably mounted in the casing 16, and theassembly includes a tubular member 32 which extends into the interior ofthe snap-acting capsule 20 and bears against the central portion of theinner face of the diaphragm 26.

The plunger assembly 30, together with the tubular member 32 are biasedagainst the diaphragm 26 by means, for example, of a back-up spring 34.The back-up spring 34 is held in place by a cup-shaped nut 36 which isthreaded into the casing 16. The nut 36 may be adjusted, so .as toadjust the force of the back-up spring 38 as it bears against theplunger assembly 30.

The tiuid pressure is introduced through the casing 16, and through thespring 34 and through the tubular member 32 into the interior of thesealed capsule 20.

When the fluid pressure exceeds a particular threshold, the diaphragm 26of the sealed capsule 20, which is in the form of a Belleville spring,snaps from the position shown in FIGURE l, to a second positiondisplaced to the left in FIGURE 1.

It will be appreciated that the switch housing 10 forms `a chamber forthe capsule 20. A header assembly 50 is threaded into the left hand endof the housing 10. The

Q header assembly supports a pair of fixed contacts 52 and 54, each ofwhich has a bent-over end portion at its right hand end, as illustrated.The xed contacts are supported in the header by bushings 56 and 58 ofany suitable insulating material.

A cup-shaped plunger 60 is slidably supported at the center of theheader assembly 50, this member 60 being composed, for example, ofstainless steel. A movable contact 62 of the assembly is supported onthe plunger 60, and is insulated therefrom by means of a suitableinsulating member 64 composed, for example, of sapphire, or other jewel,or other suitable insulating material.

An operating pin 66 is slidable in the cup-shaped plunger 60 and in themember 64. The pin 66 has a shoulder which bears against the member 64when the pin 66 is displaced to the left in FIGURE l, so as to move theVmovable contact 62 out of bridging engagement with the xed contacts 52and 54.

It will be observed that the movable contact 62 has a central bossportion 62a which normally extends between the extremities of the fixedcontacts 52 and 54. This boss on the movable contact forms a protectiveskirt, and serves to prevent arcing between the extremities of the xedcontacts.

Previously, it had been found that splattering, which takes place whenthe circuit is first broken, had a tendency to bridge over theinsulation formed by the sapphire member 64. The portion 62a of themovable contact 62 prevents splattering from reaching a location whereit can bridge over the member 64. This boss has the effect of raisingthe breakdown voltage of the assembly, and especially between the xedcontacts 52, 58 and the operating pin 66 which is in contact with theremainder of the assembly.

The arcing between the contacts can also be inhibited by introducing agas into the interior of the housing 10, that is, into the chambercontaining the capsule 20. This gas may, for example, take the form ofnitrogen having an absolute pressure in a range, for example, of from 2p.s.i. to atmospheric.

Any tendency for the aforesaid arcing to take place can be inhibited, ofcourse, by maintaining a high vacuum within the assembly. However, sucha high vacuum is diicult to achieve and maintain, on a practical andeconomical basis. For that reason, it has been found a simple expedientto fill the switch chamber with nitrogen of an absolute pressure of from6-8 p.s.i. for arc quenching purposes.

The nitrogen also has the advantage of being temperature compensating.The elastic characteristics of the capsule undergoes slight changes withvariations in environmental temperature conditions. This has a tendencyto create operational errors in the mechanism. However, it has beenfound that the thermo-elastic changes of the capsule under such varyingtemperature conditions can be negated by the corresponding effect thetemperature changes has on the nitrogen filling the switch chamber.

For example, and as Vshown in FIGURE 4, assuming that the chamber isevacuated, the curve of pressure versus diaphragm displacement wouldfollow the curve A yat a relatively low temperature, and would followthe curve B at a relatively high temperature. The introduction of gas,such as nitrogen, into the chamber, tends to maintain the two curves Aand'B relatively close to one another, so that the operatingcharacteristics of the switch are relatively independent of ambienttemperature.

The right hand end, of the operating pin 66 is positioned adjacent thediaphragm 26 of the `capsule 20. When the uid pressure introduced in tothe casing 16 exceeds a certain threshold, the diaphragm 26rsnaps to theleft in FIGURE 1, thereby moving the pin 66 and causing it to move themovable Contact 62 out of engagement with the Vends of the xed contacts52 and 54.

,A ,small gap is provided at the aforesaid shoulder of the pin 66, so asto permit a slight movement of the diaphragm 26 beforel it encounters aload. This serves to overcome initial inertia effects in the assembly.This gap, for example, may be of the order of .001 inch.

A spring 70 bears against the inner surface of the cupshaped plunger 60thereby biasing the plunger to the right in FIGURE l. The spring 70 isthe contact loading spring, and it determines the physical resistance tobe exerted by the movable contact 62 against movement thereof by thediaphragm 26.

The force exerted by the contact loading spring 70 is determined by anut 72 which is threaded into the header assembly 50. A lock -nut 74 isalso provided to hold the nut '72 -in place.

In addition, a threaded shaft 76 extends into the center of the headerassembly, and the right hand end of the shaft 76 is displaced apredetermined amount from the left hand end of the operating pin 66.`

The shaft 76 provides an adjustable stop, determining the extent towhich the fluid pressure in the capcule 20 will bias the diaphragm 26 tothe left in FIGURE l, and also determining the extent of opening of themovable contact 62. Y

A pair Iof terminal pins 80 and 82 are mounted in the casing 12 inappropriate insulating bushings 84 and `86. These pins extend into therespective fixed contacts 52 and 54, `so that -an electrical connectionmay be established to the Switch.

As mentioned above, one of the principal advantages of the doublediaphragm snap-acting capsule assembly 20 is that the stresses at theperipheral edge of the snapacting diaphragm may be decreased to a largeextent, as compared with the single diaphragm construction. The stressesaround the periphery of the single diaphragm type of unit, where thediaphragm is mounted in the casing, for example, have a tendency toexceed the yield point of the material of the diaphragm, so thatdegradation of the switch rapidly occurs.

The construction shown in FIGURE l, wherein the capsule 20 includes arst Idiaphragm 24 welded to thc casing 16, and includes a seconddiaphragm 26 welded to the diaphragm 24 at its peripheral edge, is suchthat no unduly high stresses are set up at the periphery of thesnap-acting diaphragm 26, when it is snapped. from one condition to theother.

In pressure-responsive switches of the type under consideration, thediaphragm displacement generally follows a curve, such as shown inFIGURE 5. Starting at point A, the unrestrained diaphragm snaps to itssecond position C, and a restrained diaphragm snaps to `a pointsomewhere between A a-nd C, this latter point being determined by theposition at which the end of pin 76 is contacted by operating pin `66.In actual switch assemblies, the stop is positioned at a pointconsiderably closer to A than to C.

The :pressure in the diaphragm is assumed to be the actuating pressure,and its magnitude at all times will be determined by the magnitude ofthe pressure source, with the effects of volume change within thediaphragm having a very small, if any, effect.

Theline passing through the point B and the line passing through thepoints A and C define an area known as the dead band of the switch.

When the pressure applied to the unrestrained diaphragm is decreasedfrom C, it will snap back to the position marked on FIGURE 5 as D. Arestrained diaphragm, restrained from instance at point E, would snapfrom A to E on increasing pressure. With decreasing pressure, when thepressure magnitude has reached the level indicated at F, the diaphragmwill snap -back to position G, the pressure magnitude being determinedto `a large degree by positioning of the stop or pin 76.

The dead band of the switch defines, therefore, the difference inpressure between the pressure required to actuate the switch from lafirst condition to a second condition, and the different, lowerpressure, required before the switch will return to its first position.

The free or initial dead band of the capsule 20 may, for example, bemade to be around 8 p.s.i. This is the dead band, for example, whichwould exist if there were no external forces on the capsule 20 fromeither the right or the left in FIGURE 1. In any event, the initial deadband is made to be from two to six times as large as the final desireddead band, under usual circumstances.

The tinal dead band is arrived -at during assembly by selecting a spring34 that has ythe required spring rate and by adjustment of pin 76 whichdetermines the amount of over-center travel of the capsule. Theincreasing pressure switch point is established by adjusting the nut 36which controls the force with which the spring 34 causes the tubularmember 32 to bear against diaphragm 26.

In a constructed embodiment of the invention, for example, the tinaldesired dead band was of the order of 4 p.s.i., so that the initial deadband was designed to be anywhere from e-ight to 24 p.s.i. Then the finaldead band was provided by the suitable adjustments described above.

The design of the constructed embodiment was such that the diaphragm 26would normally snap over at an applied presure of the order of 170-175p.s.i. The snapover point was then lowered by increasing, for example,the assisting force exerted by the spring 34, this being achieved byadjustment of the nut 36.

It is evident, therefore, that suitable adjustment of nut 36 supportingspring 34 can precisely set the snapover point or increasing pressureswitch point of the switch, and that the spring rate of spring '34 andproper adjustment of stop pin 76 will determine the dead band. Thefunction of spring 70 is largely parasitic in nature, and basically isused for maintaining minimum contact pressure.

It is to be noted lthat the st-op shaft 7'6 can also be adjusted todetermine the dead band. That is, this shaft provides the amount ofdisplacement possible by the diaphragm 26, and thereby determines theextent to which the iiuid pressure must be decreased, in order to permitthe diaphragm t-o return to its original state.

The position of the entire switch contact assembly with respect to thecapsule 20 may be adjusted, by initially threading the header 50 intothe housing 10 so that it has a desired placement therein. Then, theheader can be sealed to the housing by means, for example, of spotwelds, such as the weld 51. The setting of the header assembly placesthe operating point of the capsule 20 at the desired point on the curveof FIGURE 5.

In adjusting the assembly of FIGURE l, the nut 72 is first adjusted inthe header assembly 50, after the header assembly has initially beenadjusted land sealed by the welds S1. The adjustment of the nut 72determines the compression to be applied to the movable contact 62 bythe spring 70, thereby adjusting the contact pressure of the switch.

An initial adjustment of the shaft 76 is made to give somewhat greatertravel to the operating pin 66 than is ultimately desired. Theadjustin-g nut 36 adjusts the compression force of the spring 34 to givethe proper snapover point of the diaphragm 26.

The header assembly 50 is then threaded into the -housing until the pin66 has a very slight clearance from the diaphragm 26, to give thecapsule a chance to move and over-come inertia before it has to do anywork. Then, 4a final adjustment of the nut 36 is made precisely to tixthe snap-over pressure, and a final adjustment of the stop shaft 76 ismade to tix the dead band span of the switch. T-he shaft 76 is thenlocked by t-he nut 74.

The embodiment of the pressure switch shown in FIG- URE 2 is generallysimilar to the embodiment shown in FIGURE 1. However, in the latterembodiment, the backup spring 34, design-ated 34a in FIGURE 2, has beentransferred out of the pressurized fiuid area, and has been placed onthe other side of the capsule 20.

This latter embodiment has an advantage in that it removes the back-upspring from contact with the pres- 6 surized fluid, in that thepressurized tiuid often has a tendency to contaminate the springmaterial, when it comes in contact with the spring.

In the switch of FIGURE 2, like components which are the same as thoseof FIGURE l havel been designated by the same numbers. As before, thecapsule 20 is disposed in the chamber formed by the housing 10 and theend casing. The right hand end casing is now ldesignated 16a, and it mayhave the same configuration `as the casing 16 shown in FIGURE 1.However, the spring 34 is removed, so that the casing 16a forms merelyan orifice into the interior of the capsule 20, as shown.

In the latter embodiment, the loading spring, designated 70a bearsdirectly yagainst an insulating disc 100 which, in turn, lbears againstthe movable contact 62. The movable contact is mounted on the operatingpin 66a by the sapphire insulating Amember 64.

The operating pin 66a is integral with a plunger 102 which receives theIback-up spring 34a. The back-up spring 34a may be adjusted by a nut 104which is threaded into the header lassembly 50a and which is threaded onthe adjustable pin 76. A lock nut 106 is also provided.

In the illustrated embodiment, the operating pin 66a is in its extremeposition to the left in FIGURE 2, a-nd it bears against the right handend of the stop shaft 76. As in the previous embodiment, the shaft 76 isadjustable to establish the amount of deection of the capsule 20 and theresulting dead band of the switch.

In the embodiment of FIGURE 2, the spring 34a is on the opposite side ofthe capsule 20, and its adjustment oppose the actu-ation of thediaphragm 26 to the left in FIGURE 2, whereas it assists the deliectionto the left in FIGURE l. In FIGURE 2, the spring 34a loads the diaphragmdirectly with the spring 70a, the contact loading spring, serving thesame function as the spring 70 in FIG- URE l. In a like manner, thespring 34a serves a similar Afunction as the spring 34 in FIGURE 1. Thebasic difieren-ce is that with increasing spring force, spring 34a tendsto raise lthe diaphragm snap-over pressure, whereas increasing force onthe diaphragm by spring 34 tends to -decrease increasing pressure switchpoint.

The embodiment of FIGURE 3 is generally similar to that of FIGURE 2.However, in the latter embodiment, the capsule 20 has been reversed, andit is mounted on the housing 10, rather than on the casing 16.

Since the housing and casing each have a somewhat differentconfiguration in the embodiment of FIGURE 3, the housing is designated10a, and the casing is designated 16a.

It will be observed that the operating pin 66a extends into the capsule20 to be engaged by the inner surface of the diaphragm 26. Thepressurized uid is introduced through the orifice formed by the endcasing 16a, and into Va chamber 200 which is sealed by the capsule 20.

In the modification shown in FIGURE 3, the pressur-' ized fluid isapplied to the outside of the capsule 20, yrather than the inside. Thishas an Iadvantage in that the pressurized iiuid does not reach the innerweld 22a of the capsule. Under some conditions, the pressurized iiuidhas an errosive effect on the weld, so that it may have a tendency tofail.

The movable contact of the latter embodiment is designated 62b, and ithas ya somewhat different configuration from the movable contact of theprevious embodiment. The movable contact is formed as an annular ringcomposed, for example, of silver about lan insulating armature 202, thearmature being supported on the operating pin 66a by means, for example,of a nut 204.

The contact loading spring 70a bears against the member 202 which, forexample, may -be composed of sapphire. The annular movable contact 62bengages the fixed contacts 52 and S4, when the switch is in its closedcondition.

The embodiment of the invention shown in FIGURE 3 may be modified toinclude the spring assembly 30, 34,

36 of the embodiment of FIGURE l in the pressure inlet orifice. Thisinclusion permits linear spring loading of the diaphragm from thepressure side of the unit.

With such a modification, the advantage is gained of being able toadjust the increasing pressure switch point of the capsule either to ahigher magnitude by being able to apply increased force from the spring34a, or to a lower magnitude by increasing the spring force on thediaphragm by compressing spring 34 from the pressure side.

Two main advantages result from the latter configuration. The first isthe ability to use capsules having a greater spread of increasingpressure snap magnitudes, thereby increasing producibility. This isbecause the increasing pressure switch point can be increased ordecreased by adjustment.

In the single spring load diaphragm coniiguration, on `the other hand,there is only the choice of one or the other.

The second advantage stems from the fact that a third variable isavailable in the basic spring system. This permits better spring rateadjustment so as to obtain better dead band control and adjustment. Thisallows greater utilization of snap capsules having high initial deadbands and results in greater producibility.

It has been established that certain advantages would stem from having astop on the pressure side that would Y limit diaphragm travel. Thiswould make possible presetting a diaphragm in the unpressurizedcondition to 4a position on the curve shown in FIGURES between A and B.In this arrangement, having the diaphragm stop above and below or on thepressure side and on the reference side would permit successfuloperation in the event extremely narrow dead bands must be provided. Inthis case, final switch performance would be as shown in FIGURE 6.

The stop on the pressure side will limit movement to a position shown ata in FIGURE 6 with the stop adjusted on the reference side limitingcapsule movement in the snapped-over condition at b. Increasing pressureactuation would occur at the pressure magnitude present -at a, snappingfrom a to b. Decreasing pressure would snap the diaphragm back from d toc when the curve is reached at d. Dead bandwould be the difference ofthe pressure magnitude present at d and that present at a.

In other words, operation is completely on the negative slope side ofthe snap capsule, as shown on the initial capsule pressure vs.defiection curve. It is obvious that in this latter arrangement `capsulemovement is considerably restrained from that existent in otherconfigurations. Advantages of this type of configuration would begreater useful life due to increased fatigue resistance, and greaterstability of performance.

In other words, to summarize, this latter type of switch would providegreater accuracies and better dead band control, particularly ifextremely narrow dead bands are required, maintaining these propertiesover an increased useful life, both as to total cycles as well as thetime element.

The invention provides, therefore, an improved pressure-responsiveswitch which is durable in its construction and reliable in itsperformance, and which has the capabilities of operating over longperiods of time without failure.

While particular embodiments of the invention have been shown anddescribed, modifications may be made. It is intended in the claims tocover all modifications which come within the scope of the invention.

What is claimed is:

1. A snap-acting pressure responsive switching assembly which isactuable to a first condition in response to a first pressure and whichis actuable to a second condition in response to a second pressure, saidswitching assembly including: a housing enclosing a chamber and definingan orifice; a disc-shaped yieldable supporting diaphragm mounted in saidchamber, said diaphragm having an aperture therein and being affixed tosaid housing at the periph ery of said orifice and of said aperture withsaid aperture aligned with said orifice; a disc-shaped snap-actingdiaphragm mounted in said chamber in facing relationship with saidsupporting diaphragm and sealed thereto at the peripheral edge of saidsupporting diaphragm and snapacting diaphragm; a pair of elongated fixedcontacts mounted in said housing in spaced insulated relationship and.extending into said chamber, said fixed contacts having end portionsextending essentially parallel to the plane of said snap-actingdiaphragm and spaced therefrom; a plunger member slidably mounted insaid housing for reciprocal motion essentially perpendicular to theplane of said snap-acting diaphragm; a movable contact mounted on saidplunger'member for selective bridging engagement with said end portionsof said fixed contacts; an operating pin mounted on said plunger memberand extending perpendicular to said snap-acting diaphragm to a positionadjacent the surface thereof so as to move said movable contact in onedirection relative to said end portions of said fixed contacts when saidsnap-acting diaphragm snaps to one operating condition; and resilient`means mounted in said housing for moving said movable contact in theopposite direction relative to said end portions of said fixed contactswhen said snap-acting diaphragm snaps to a second operating condition.

2. The combination defined in claim 1 and which includes adjustablemeans mounted in said housing for controlling the force exerted bysaidresilient means.

3. The combination defined in claim 1 in which said movable contact hasa central portion which normally extends between the extremities of saidend portions of said fixed contacts to prevent arcin-g ltherebetween.

4. The combination defined in claim 1 and which includes a pinadjustably mounted in said housing in axial alignment with Said plungermember vto provide a stop y therefor and thereby tolimit the extent oftravel of said snap-acting diaphragm in one of the operating conditionsthereof.

5. The combination defined in claim 1 and which includes a tubularmember slidably mounted in said orifice and extending through saidaperture into engagement with said snap-acting diaphragm, spring meanspositioned in said orifice and engaging said tubular member to bias saidtubular member against the surface of said snap-acting diphragm, andadjustable means positioned in said orifice and engaging said springmeans to control the force exerted by said tubularl member on saidsnap-acting diaphragm.

6. The combination defined in claim 1 in which said operating pinextends through said aperture in said supporting diaphragm into positionwith its end adjacent the inner surface of said snap-acting diaphragm.

References Cited UNITED STATES PATENTS 1,684,530 9/1928 Bast I 200-83 X1,790,564 l/l931 Williams 200-83 l2,615,104 10/1952 Hosford 20G-832,632,119 3/1953 Schneider 20G-83 X BERNARD A. GILHEANY, PrimaryExaminer. H. B. GII/SON, G. MAIER, Assistant Examiners.

1. A SNAP-ACTING PRESSURE RESPONSIVE SWITCHING ASSEMBLY WHICH ISACTUABLE TO A FIRST CONDITION IN RESPONSE TO A FIRST PRESSURE AND WHICHIT ACTUABLE TO A SECOND CONDITION IN RESPONSE TO A SECOND PRESSURE, SAIDSWITCHING ASSEMBLY INCLUDING: A HOUSING ENCLOSING A CHAMBER AND DEFININGAN ORIFICE; A DISC-SHAPED YIELDABLE SUPPORTING DIAPHRAGM MOUNTED IN SAIDCHAMBER, SAID DIAPHRAGM HAVING AN APERTURE THEREIN AND BEING AFFIXED TOSAID HOUSING AT THE PERIPHERY OF SAID ORIFICE AND OF SAID APERTURE WITHSAID APERTURE ALIGNED WITH SAID ORIFICE; A DISC-SHAPED SNAP-ACTINGDIAPHRAGM MOUNTED IN SAID CHAMBER IN FACING RELATIONSHIP WITH SAIDSUPPORTING DIAPHRAGM AND SEALED THERETO AT THE PERIPHERAL EDGE OF SAIDSUPPORTING DIAPHRAGM AND SNAPACTING DIAPHRAGM; A PAIR OF ELONGATED FIXEDCONTACTS MOUNTED IN SAID HOUSING IN SPACED INSULATED RELATIONSHIP ANDEXTENDING INTO SAID CHAMBER, SAID FIXED CONTACTS HAVING END PORTIONSEXTENDING ESSENTIALLY PARALLEL TO THE PLANE OF SAID SNAP-ACTINGDIAPHRAGM AND SPACED THEREFROM; A PLUNGER MEMBER SLIDABLY MOUNTED INSAID HOUSING FOR RECIPROCAL MOTION ESSENTIALLY PERPENDICULAR TO THEPLANE OF SAID SNAP-ACTING DIAPHRAGM; A MOVABLE CONTACT MOUNTED ON SIDPLUNGER MEMBER FOR SELECTIVE BRIDGING ENGAGEMENT WITH SAID END PORTIONSOF SAID FIXED CONTACTS; AN OPERATING PIN MOUNTED ON SAID PLUNGER MEMBERAND EXTENDING PERPENDICULAR TO SAID SNAP-ACTING DIAPHRAGM TO A POSITIONADJACENT THE SURFACE THEREOF SO AS TO MOVE SAID MOVABLE CONTACT IN ONEDIRECTION RELATIVE TO SAID END PORTIONS OF SAID FIXED CONTACTS WHEN SAIDSNAP-ACTING DIAPHRAGM SNAPS TO ONE OPERATING CONDITION; AND RESILIENTMEANS MOUNTED IN SAID HOUSING FOR MOVING SAID MOVABLE CONTACT IN THEOPPOSITE DIRECTION RELATIVE TO SAID END PORTIONS OF SAID FIXED CONTACTSWHEN SAID SNAP-ACTING DIAPHRAGM SNAPS TO A SECOND OPERATING CONDITION.